This invention relates to an electronic musical instrument in which a musical tone generating circuit which does not belong to any keyboard is provided so that it may be used commonly for any keyboard as required.
Normally, in a conventional electronic musical instrument, musical tone generating circuits are provides for respective keyboards so as to provide musical tones having tone colors which are different from one another depending upon the kind of keyboard. in other words, different musical tone generating circuits are provided for different keyboards, and, accordingly, when a key in a keyboard is depressed, a musical tone generating circuit provided for the keyboard produces a musical tone having a tone color peculiar to that keyboard.
A technique called "inter-keyboard coupler" is known in the art. In this technique, a musical tone generating circuit which belongs to one keyboard only as described above is driven by the key operation of another keyboards, so that the tones of the keyboard operated actually and the tones of the keyboard not actually operated are produced together. However, this "inter-keyboard coupler" has the difficulty that musical tones having all tone colors peculiar to the coupled keyboard are produced in response to the key operation on the actually operated keyboard and it is impossible to select a part of the tone colors; that is, by the key operation of keyboard, all the musical tone generating circuits for the coupled keyboard are driven.
For instance, a "coupler" in which musical tone generating circuits for an upper keyboard are driven by key operation of a lower keyboard will be described. If in this case a piano tone color and a clarinet tone color are selected for the upper keyboard and a flute tone color is selected for the lower keyboard, then tones having the piano tone color and clarinet tone color are produced by the key operation of the upper keyboard, and tones having the flute tone color, piano tone color and clarinet tone color (that is, both of the upper keyboard tones and the lower keyboard tones) are produced by the key operation of the lower keyboard. Thus, with the "inter-keyboard coupler", it is impossible to produce only tones having the piano tone color by the key operation of the upper keyboard and to produce only tones having the flute tone color and clarinet tone color by the operation of the lower keyboard.